1. Field of the Invention
The present invention relates to a vehicle diesel engine and a method of controlling the vehicle diesel engine.
2. Description of the Related Art
A vehicle diesel engine has a diesel particulate filter (DPF) in its exhaust passage to trap particulate matter (PM) contained in exhaust gas through the DPF in order to minimize exhaust emissions to the atmosphere. As the amount of PM deposits on such DPF increases, the filtering capability of the DPF decreases. Therefore, when the amount of PM deposits exceeds a predetermined amount, the DPM is heated to burn the PM deposits on the DPF to recover the filtering capability. The fuel injection valve supplies fuel to a combustion chamber of the engine through a primary fuel injection. Fuel may also be supplied through the fuel injection valve to a catalyst, such as an oxidation catalyst or an NOx storage reduction catalyst, provided in the exhaust passage upstream of the DPF, via a secondary fuel injection after the primary fuel injection. The secondary fuel injection is called post fuel injection. This allows the DPF to be heated by the heat generated through the oxidization of the fuel supplied to the catalyst.
However, the post-injected fuel is not burned in the combustion chamber. Thus, some of the fuel, which clings to the inner wall of the cylinder after being injected from the fuel injection valve, is mixed with engine oil in the oil pan located below the cylinder. Consequently, this dilutes the engine oil, which reduces engine oil lubrication performance. Thus, there arises a problem that the engine may seize up.
Some vehicle diesel engines are proposed in order to prevent the problem with the engine, such as seizing up due to the engine oil dilution. As described in Japanese Patent Application Publication No. 2005-307778 (JP-A-2005-307778), the vehicle diesel engine is designed to detect the degree of dilution of engine oil and alert a driver when the degree of dilution of engine oil is equal to or greater than an allowable degree at which an oil change is required, and simultaneously prohibit post fuel injection. This encourages the driver to change oil, while keeping the engine oil from becoming quickly diluted with fuel by prohibiting post fuel injection, and therefore, prevents the engine from seizing up.
The vehicle diesel engine has an exhaust gas purification device that alerts a driver when the degree of dilution of the oil exceeds an allowable maximum level, and simultaneously prohibits the above described post fuel injection. This ensures that the engine is prevented from seizing due to the oil dilution.
However, the driver may not always change oil immediately after the oil change alert is issued. Assuming that no oil change has been done for a prolonged period after the oil change alert or the prohibition of post fuel injection, the filtering capability of the DPF will not be regenerated during that period. During this period, the filtering capability is reduced significantly. Consequently, in addition to deterioration of the PM purification performance, another unavoidable problem arises, that is, increased exhaust resistance due to the clogging of the PM filter.
The post fuel injection is conducted sometimes for the purpose of preventing the temperature of the exhaust gas purification catalyst, such as oxidation catalytic converter and NOx catalytic converter for purifying NOx, from falling below the temperature at which the catalyst is active. The post fuel injection is also conducted sometimes for the purpose of supplying fuel as a reductant to reduce NOx. Therefore, the above problems are shared not only with PM filters for trapping PM, but also with general exhaust gas purification devices including the oxidation catalytic converter and the NOx catalytic converter.